The effect of trans and positional isomers of octadecenoic acid on mammalian metabolism and in particular their effect on cholesterol metabolism through reduced capacity to clear their cholesterol esters in the circulating plasma lipoproteins will be studied. The intestines as a source of cholesterol esters of trans fatty acids, i.e. cholesteryl elaidate will be investigated by studying lymph lipoproteins from cannulated rats which 1) had been fed hydrogenated fats, 2) given orally radioactive mixtures of H3-positional isomers of oleic acid and 1-C14 -oleic acid, and 3) fed orotic acid and hydrogenated fat. Work has already been completed on plasma lipoproteins in rats fed trans fatty acids (starved and fed rats) and rats fed trans fatty acids and orotic acid. The transport and metabolism of H3-labelled positional isomers relative to 1-C14-oleic acid into plasma lipoproteins after intravenous administration will be studied. Monitoring the metabolism will be done by the dual label technique. Work has been completed about the 1) in vitro incorporation of cis-octadecenoic acids in rat liver mitochondria; 2) metabolism of H3-labelled cis-octadecenoic acids in the rat, and 3) distribution of dietary elaidic acid in subcellular particles of rat liver. Rat liver lysosomal cholesterol esterase has been solubilized and partially purified. Efforts will continue to purify the enzyme to homogeneity and compare it to the cholesterol ester hydrolyzing enzyme from the microsomal supernatant. In continuation of previous work on the lecithin cholesterol acyl transferase (LCAT) fatty acid specificity, LCAT from several species with different susceptibility to cholesterol induced atherosclerosis will be tested against lecithins labelled with different fatty acids at the beta-position. BIBLIOGRAPHIC REFERENCE: D. S. Sgoutas, R. Jones, and M. Leight. Distribution of Dietary Elaidic Acid in Subcellular Particles of Rat Liver. Int. J. Biochem. 1974, 4, 437.